Well-established power distribution systems exist throughout most of the United States, and other countries, that provide power to customers via power lines. With some modification, the infrastructure of the existing power distribution systems can be used to provide data communication in addition to power delivery, thereby forming a power distribution communication system. In other words, existing power lines that already have been run to many homes and offices can be used to carry data signals to and from the homes and offices. These data signals are launched or retrieved from the power lines at various points in the power distribution communication system, such as, for example, near homes, offices, Internet service providers, and the like.
While the concept may sound simple, there are many challenges to overcome in order to use power lines for data communication. Power distribution systems include numerous sections, which operate at different voltages. The transition from one section to another typically is accomplished with a transformer. The sections of the power line distribution system that are connected to the customers typically are low voltage (LV) sections having a voltage between about 100-800 volts, depending on the system. In the United States, the low voltage section typically operates with two legs each 120 volts above ground The sections of the power distribution system that provide the power to the low voltage sections are referred to as the medium voltage (MV) sections. The voltage of the MV section is in the range of 1,000 Volts to 100,000 volts and typically 7.6 kilovolts (kV) to neutral (13.2 kV between phase conductors). The transition from the MV section to the LV section of the power distribution system typically is accomplished with a distribution transformer, which converts the higher voltage of the MV section to the lower voltage of the LV section.
Power system transformers are one obstacle to using MV or LV power distribution lines for data communication. Transformers are designed for conversion of power at low frequencies (i.e. 50 or 60 Hz) and present complex and usually undesirable series and shunt impedances that can be detrimental to data signals at higher frequencies useful for communications. As such, power distribution communication systems face the challenge of passing the data signals around (or sometimes through) the distribution transformers.
To communicate data signals over the medium voltage power lines, the system needs a method of coupling to and from those lines. As discussed, medium voltage power lines may operate from about 1000 V to about 100 kV, and can deliver large amounts of energy. Consequently, coupling to a medium voltage power line gives rise to safety concerns for the persons installing the coupling device.
The coupling device should be designed to provide safe and reliable communication of data signals with a medium or high voltage power line—carrying both low and high current—in all outdoor environments such as extreme heat, cold, humidity, rain, wind, high shock, and high vibration. Also, coupling around the distribution transformer—such as in transformer bypass systems—raises concern that dangerous MV voltage levels may be inadvertently conducted to the customer premises on the low voltage power line, which the coupling device should prevent. In addition, a coupling device should be designed so that it does not significantly compromise the signal-to-noise ratio and facilitates bi-directional communication. In addition, the coupling device (or coupler as referred to herein) should enable the transmission and reception of broadband radio frequency (RF) signals used for data transmission on MV lines
Various embodiments of the coupler of the present invention may provide many of the above features and overcome the disadvantages of the prior art.